Supersonic and hypersonic wind tunnels presently used for ground testing of aircraft concepts are limited in their usefulness for purposes of studying boundary layer stability and transition by premature transition of the model boundary layer. This boundary layer transition is caused by noise or pressure fluctuations radiating from the turbulent boundary layer on the tunnel wall and impinging upon the model. There are two basic methods of preventing or reducing the radiated noise. First, because it is the turbulent boundary layer that radiates noise versus a laminar boundary layer that does not radiate noise, a laminar boundary layer on the tunnel wall is desired. This can be accomplished by various techniques, one of which consists of using longitudinal rods for the nozzle walls so that suction can be applied to the boundary layer thus maintaining a laminar boundary layer and is more fully described in NASA TMX-2566 published July 1972.
The second method of reducing the radiated noise is by shielding the model from the turbulent tunnel wall boundary layer. The present invention is directed to a system employing this method.
It is therefore an object of the present invention to provide an improved wind tunnel system for testing models subjected to supersonic and hypersonic fluid flow.
Another object of the present invention is an improved test section for a supersonic or hypersonic wind tunnel wherein the model tested is shielded from the noise radiated by the turbulent tunnel wall boundary layer.
Another object of the present invention is to provide a vacuum chamber in fluid communication with and surrounding the test chamber of a wind tunnel to remove some of the boundary layer from the test chamber as formed and thereby help maintain laminar tunnel wall boundary layers.
Another object of the present invention is to provide a test facility that shields the test model from noise radiated by the turbulent tunnel wall boundary layers in a supersonic or hypersonic wind tunnel.
According to the present invention, the foregoing and additional objects are obtained in the present invention by providing a slightly tapered rectangular test chamber in a supersonic or hypersonic wind tunnel wherein the test chamber walls are formed of spaced rod elements and surrounded by a vacuum chamber. The vacuum chamber provides a vacuum source to extract some of the boundary layer formed along the rod elements within the test chamber through the space between the rods and thereby delay the tendency of the rod boundary layers to become turbulent.